Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $219.70   6.202%   $233.3258   $233.33   $233.35   $233.30  
  Purchase #2 $142.32   5.803%   $150.5788   $150.58   $150.60   $150.60  
  Purchase #3 $182.42   11.780%   $203.9091   $203.91   $203.90   $203.90  
  Purchase #4 $62.98   5.570%   $66.488   $66.49   $66.50   $66.50  
  Purchase #5 $230.95   3.683%   $239.4559   $239.46   $239.45   $239.50  
  Purchase #6 $158.27   6.140%   $167.9878   $167.99   $168.00   $168.00  
  Purchase #7 $194.36   10.739%   $215.2323   $215.23   $215.25   $215.20  
  7 purchase totals = $1,191.00       $1,276.9777   $1,276.99   $1,277.05   $1,277.00